Robotic cleaning systems are known in the art and may typically include a rechargeable battery-powered, autonomously travelling robot cleaner and a stationary base station. The battery enables the robot's temporary autonomy, but requires periodic charging at the base station. The robot and its base station may therefore be fitted with means configured to ensure that the robot cleaner is capable of locating the base station and returning thereto before its battery is exhausted.
In many known robotic cleaning systems, such as the one disclosed in U.S. patent application Ser. No. 11/486,284, use is made of a stationary base station fitted with a plurality of signal transmitters, and a mobile robot cleaner fitted with one or more sensors for receiving the signals transmitted by the signal transmitters on the base station. The signals of the various signal transmitters may differ in code, and each of the signals may be transmitted from the base station in a particular direction so as to be receivable in a certain, generally cone-shaped region extending from the base station. Accordingly, the signals may enable the robot to determine its position relative to the base station, and in particular its presence in a certain region, based on the encoding of the signals it receives.